Determination of the Adsorption Isotherms of Hydrogen and Deuterium Isotopes on a Pt−Ir Alloy in LiOH Solutions Using the Phase-Shift Method and Correlation Constants

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• 作者：Jinyoung Chun ; Nam Y. Kim ; Jang H. Chun
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2010
• 出版时间：December 9, 2010
• 年：2010
• 卷：55
• 期：12
• 页码：5598-5607
• 全文大小：325K
• 年卷期：v.55,no.12(December 9, 2010)
• ISSN：1520-5134

文摘

The phase-shift method and correlation constants, which are unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the phase shift (90° ≥ −φ ≥ 0°) versus electric potential (E) behavior for the optimum intermediate frequency and the fractional surface coverage (0 ≤ θ ≤ 1) vs E behavior, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On a Pt−Ir alloy (90:10 mass ratio) in 0.1 M LiOH (H₂O) and 0.1 M LiOH (D₂O) solutions, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants (K), interaction parameters (g), standard Gibbs energies (ΔG_θ^°) of hydrogen (H) and deuterium (D) adsorption, and rates of change (r) of ΔG_θ^° of H and D with θ have been determined and are compared using the phase-shift method and correlation constants. The value of K decreases in going from H₂O to D₂O. The values of K for both H and D increase with increasing E and θ. Over the θ range (i.e., 1 ≥ θ ≥ 0), the value of K for H is 3.7 to 4.1 times greater than that for D. For 0.2 < θ < 0.8, a lateral attractive (g < 0) or repulsive (g > 0) interaction between the adsorbed H or D species appears. The duality of the lateral attractive and repulsive interactions is a unique feature of the adsorbed H and D species on Pt, Ir, and Pt−Ir alloys in acidic and alkaline H₂O and D₂O solutions.